1. The 3D Medical Imaging using Proton Computed Tomography
Loma Linda University
Dr. Reinhard Schulte, MD, V. Bashkirov
and
Santa Cruz Institute for Particle Physics, UCSC
H. Sadrozinski, R. Johnson, T. Platz, A. Zatserklyyaniy
And
Northern Illinois Univ. (image reconstruction)
G. Coutrakon, N. Karonis, C. Ordonez
Baylor University (image reconstruction)
K. Schubert, B. Schultze
University of Wollongong, Medical Physics Dept.
V. Giacometti ( image reconstruction)

2. In: Radiological use of fast protons. Wilson R. R
In: Radiological use of fast protons. Wilson R. R., Radiology 45, , (1946)
Described the advantages of proton and ion beams for radiation therapy.
Suggested several techniques that are still in use today.
Robert Wilson

4. Proton Gantry is also needed for Proton CT
Proton beams can be delivered throughout 360 degrees around the patient using a Gantry
Proton Gantry is also needed for Proton CT
Retract nozzle to insert pCT detector

5. Proton treatment plan for breast tumor
Proton treatment plan for breast tumor. Errors in proton stopping powers can lead to heart and lung dose beyond the target due to proton range errors
Proton Treatment Plans currently use X-ray CT for proton RSP values. These produce range errors of 3.5%

6. Slide courtesy of Reinhard Schulte, Loma Linda University

7. Relative stopping power and electron density
To first order electron density=RSP

8. RSP  WEPL  Relative Dose
To calculate dose and P+ range we need relative stopping power (RSP) in each 3D voxel of the patient along the proton path

9. Slide courtesy of Reinhard Schulte, Loma Linda Univ.

10. (Moyers, Medical Dosimetry, Oct 2010)
Proton RSP’s are derived from x-ray linear attenuation coefficient (μ) in tissue substitutes with “reasonable” success.
(Moyers, Medical Dosimetry, Oct 2010)

11. Advantages of proton CT over X-ray CT
Decrease the range error from 3% to 1% for better electron density map for proton Tx Planning => better dose accuracy to target volume. Range error is caused by RSP error
Reduce or eliminate CT artifacts due to metal/dental implants with high Z materials
Lower dose ( factor 3) to patient relative to X-ray CT
pCT head dose = 1.4 mS = 140 mrem; X-ray CT dose=500mrem
pCT imaging could replace all other x-ray imaging for patient alignment verification before Treatment
Spatial resolution will be worse than x-ray CT, but density resolution will be better.

12. High Level Proton CT Detector requirements
Head Imaging Volume– 20 cm diam. Cylinder; 20 cm long
Need 100 proton tracks per voxel for a head size phantom with 4 million voxels to get 1% density or RSP resolution
Need 400 million protons fired from 0 to 3600 of rotation with scan time less than 10 min.
Data acquisition rate = 1 MHz for tracker + Calorimeter
Compact size upstream detector < 20 cm ”thick” and retractable
Spatial resolution of track < 1mm (rms)
Thin tracking detectors < 1 mm water equivalence thickness per plane. Exiting proton energy as low as 50 MeV multiple coulomb scattering.
Energy resolution of scintillator; dE/E < 2 % (i.e., not limited by energy straggling of phantom plus energy detector)
Angular resolution pointing to head < 5 mrad to get 0.5 mm

13. UC Santa Cruz Silicon Strip Detector
PIN Diode sensors:
P type implants on top, in the form of long, narrow strips
n-type Instrinsic (ultra high purity) silicon bulk
N type implants on the bottom plane
The diodes are reverse biased with +100 V applied to the back plane, and each strip is connected to ground by an integrated resistor. As a result, the bulk silicon is fully depleted.
Each strip is covered by a thin oxide layer with an aluminum strip on top, forming integrated capacitors between the p strips and the aluminum pads to which we connect the amplifiers.
8.95 cm square Hamamatsu-Photonics SSD before cutting from the 6-inch wafer. The thickness is 400 microns, and the strip pitch is 228 microns.
4/22/2016
pCT

14. Silicon-Strip Tracking Plane
Two layers of single-sided detectors are needed to measure a 3-D space point.
V-Board Measures V Coordinates
384 strips
We sawed off the sensor edges to minimize the gaps!
After cut
T-Board Measures T Coordinates
Readout ICs
4/22/2016
pCT

15. Complete Tracker Module at UCSC
Measures two 3-D space points, to give a track vector
FPGA programming cables
One DVI connector per board, for digital communication
Two V boards and two T boards
4/22/2016
pCT

16. The UCSC Tracker Readout Custom IC (“ASIC”)
Includes a lot of digital buffering and processing for the data acquisition, in addition to the 64 amplifiers and discriminators.
4/22/2016
pCT

17. Loma Linda’s 5 Stage Scintillator – Energy detector
Vladimir Bashkirov
V.A. Bashkirov, R.P. Johnson, et al., Novel Scintillation Detector Design and Performance for Proton Radiography and Computed Tomography, Med. Phys. 43, 664 (2016).
At 1 MHz rate the PMT currents are very high in the last 3 dynodes, so active bias is needed.
4/22/2016
pCT

18. UCSC Scanner 9 cm by 36 cm aperture
UCSC + LLUMC + CSSB/Baylor
UCSC Scanner
Silicon-Strip Trackers
Event Builder
protons
Energy Detector
Rotation Stage
9 cm by 36 cm aperture
Silicon strips for the tracking detectors; 228um spacing
Plastic scintillator measures proton energy E(out) after phantom
E(in)-E(out)=Energy loss WEPL through the phantom
See R.P. Johnson et.al., IEEE Trans. Nucl. Sci (2015)
Installed at Northwestern Medicine Chicago Proton Center
R.P. Johnson, et al.,, IEEE Trans. Nucl. Sci (2015).
4/22/2016
pCT

19. 1st 3D images of an object scanned by proton CT (2010) 130 million protons at 200 MeV, 90 angles cm polystyrene sphere with 3 inserts CT slice (2.5 mm) is through the diameter Image is gray scale of RSP values in 0.6 mm x 0.6 mm RSP range: 0(air)1.7 (bone)

20. Reconstructed relative stopping powers (RSP) from 3D image reconstruction of LUCY phantom
Averege RSP
(measured)
RSP
(calculated)
Polystyrene
1.037
1.035
Bone
1.62
1.65
Lucite
1.15
Air
0.05
0.001

21. UC Santa Cruz PCT Scan of Sensitom Phantom [DROP, 45 blocks, 10 iterations, l=0.1, pixel=0.75mm, slice=0.75mm]
CEO 31-Aug-16

22. UC Santa Cruz PCT Scan of Sensitom Phantom [ pixel size =0
UC Santa Cruz PCT Scan of Sensitom Phantom [ pixel size =0.75mm, slice thickness=0.75mm]
Material
RSP (from pCT)
RSP(true/meas.)
% error
Teflon
1.776
1.754
- 0.8 %
LDPE
1.000
0.980
2 %
Polystyrene
1.041
1.024
1.7%
Delrin
1.340
1.360
- 1.4 %
PMP
0.890
0.883
0.85 %

23. 1st complete head scan (CIRS model 715)
1st complete head scan (CIRS model 715). Taken with Loma Linda –UCSC Phase II scanner
Pediatric ( 5 yr. old, CIRS) head phantom used for imaging
Single reconstructed proton CT slice through lower mandible and teeth
Data acquired at 1 million events per second using a 200 MeV proton beam and 90 beam entry angles (4 deg intervals)
Total scan time < 20 min.

24. Proton CT reconstructed images of pediatric head phantom using 350 million proton trajectories distributed 0 to about vertical axis

25. Proton CT reconstructed images of pediatric head phantom using 350 million proton trajectories distributed 0 to about vertical axis

26. 16 Proton CT slices of pediatric head phantom Each slice is 2
16 Proton CT slices of pediatric head phantom Each slice is 2.5 mm thick, resolution in each slice: 0.6 x 0.6 mm
Note: There is a amalgam dental filling (upper right image) and a Gold crown on another tooth

27. X-ray CT slice ( center image) of same phantom with Gold dental crown High density inserts produce large streaking in X-ray CT

28. Summary & Conclusion
Proton CT can reduce target volume in proton therapy  less dose to healthy tissue.
Important when treating tumors close to critical structures like brain stem, optic chiasm, and spinal cord.
Proton CT also offers a several-fold dose advantage compared to x-ray CT
No streaking artifacts from high density implants or calcification.
New proton CT head scanner has been developed and is generating new images regularly with more improvements at the Chicago Proton Center.

29. Thank you for your attention
End of presentation
Thank you for your attention